Structure-activity relationship studies of phencyclidine derivatives in rats

Phencyclidine (PCP), a semirigid molecule containing a cyclohexane ring with vicinally attached aromatic and piperidine rings, produces characteristic discriminative stimulus properties and pupillary miosis in rats. The effectiveness of series of aromatic and nitrogen substituted analogs of PCP in producing PCP-liked discriminative stimuli and changes in pupil diameter was determined in rats trained to discriminate between saline and 3.0 mg/kg of PCP. Dexoxadrol and its optical isomer levoxadrol were also evaluated for purposes of comparison. Analogs in which the electron-density of the aromatic ring was increased (3NH₂-PCP) or only slightly reduced (3F-PCP) retained PCP-like activity. A loss of PCP-like activity occurred with analogs in which the electro-density of the aromatic ring was greatly reduced (3NO₂-PCP) or extended to a larger system (1NCP and 2NCP). PCP-like activity also was abolished in analogs in which the distance between the aromatic ring and the remainder of the molecule was systematically increased by one, two or three methylene units. In contrast, substitutions on the nitrogen atom altered the potency, but not the efficacy, of such analogs. Dexoxadrol produced PCP-like activity whereas its optical enantiomer levoxadrol was devoid of such activity. These findings suggest a drug receptor surface with multiple domains of subsites which recognize regions of structural overlap among the phencyclidines, dioxolanes and psychotomimetic benzomorphan derivatives.